The present research is concerned with specifying the nature of early individual differences in aggression, with determining the relationship between parenting and biobehavioral factors, and the development of different patterns of aggressive behavior. Children are studied longitudinally beginning at about one year of age, and continuing for some children until seven years of age. There are two primary sources of data. The first is mothers' observations, reported in narrative, of aggressive incidents involving the child during the daily course of events in the home. The second source of data are a series of laboratory sessions in which young children's behavior towards peers and adults is examined in a variety of settings. Preliminary analyses indicate that there are considerable individual differences in styles of aggression from as early as one year of age.